Animals can use scent as simple signs of things like “I’m scared” or “I’m stressed.” This can reach a more complex level of communication, though, if the emission of an odor changes based on the relationship of the animal putting out that scent and the one smelling it (for example, telling only your mom when you’re scared).

Fifty years ago, George Schaller (now vice president of Panthera, a wild cat conservation group) noted that the scent of a wild gorilla group leader — the silverback male — wasn’t constant. On some days Schaller could easily smell the silverback; on others, the lead male wasn’t at all stinky. Figuring out any pattern in the change in scents, however, had to wait until now, when researchers have access to wild gorilla groups that have been habituated to humans. These are animals that are wild but don’t mind being followed for days on end by scientists.

To study scent communication in wild western lowland gorillas (Gorilla gorilla gorilla), a team of trackers and researchers followed the Makumba gorilla group in the Bai Hokou Primate Habituation Camp in the Central African Republic for all of 2007. This group is named for its silverback, Makumba, and in 2007 also contained three adult females, two subadults, one blackback (an adult male), four juveniles and two infants, plus one baby that was born at the end of the year.

During the course of the year, the researchers recorded the scent of the silverback based on a “human pungency scale.” No odor was given a zero. A light scent, no stronger than the surrounding vegetation, ranked a one. A smell stronger than vegetation got a two, while an extreme odor that drowned out everything else was considered a three. Two humans had to rank an odor to be certain that the smell really was as light or heavy as each perceived it.

The researchers then matched up these scent rankings with records of the gorillas’ relationships, activity and auditory signals — everything from belches and barks to ground-slapping and chest-beating.

The silverback reeked in four different situations: when he was making sounds of distress or anger, when the group encountered another group of gorillas, when the mother of the group’s youngest infant (along with the baby) were far away and when the silverback was making “long-calling signals.” Long-calling signals are used for communicating over large distances and with gorillas outside the group.

“Silverbacks appear to use odor as a modifiable form of communication; where odor acts as a highly flexible, context dependent signaling mechanism to group members and extragroup units,” the researcher write. Michelle Klailova and Phyllis C. Lee of the University of Stirling in Scotland published their study July 9 in PLOS ONE.

This type of communication may be important for animals that live in forests, where the lead male can easily lose track of group members wandering nearby to search for food. Part of his job as leader, after all, is to protect the other gorillas. Mothers of young infants in the group may be especially at risk because rival males may try to woo the females away or even kill the babies in their coercion efforts, the researchers note.

However, it’s important to remember that this is a study of only one silverback and his group. Scientists will need to gather far more data if they are to say that western lowland gorillas are truly using scent for social communication.